JP6200064B2 - Mold substrate recycling method - Google Patents

Description

  The present invention relates to a mold recycling method, and more particularly to a mold recycling method having a porous alumina layer. The “mold” here includes molds used in various processing methods (stamping and casting), and is sometimes referred to as a stamper. It can also be used for printing (including nanoprinting).

  The present applicant has put into practical use a method of forming an antireflection film (or antireflection surface) having a moth-eye structure using a mold having a porous alumina layer, and uses the method for a display device such as a liquid crystal television. A porous alumina layer included in a mold for forming an antireflection film having a moth-eye structure (referred to as “moth-eye mold”) has a structure in which the moth-eye structure is inverted (hereinafter referred to as “inverted moth-eye structure”). The inverted moth-eye structure is constituted by micro concave portions.

The micro concave portion of the porous alumina layer of the moth-eye mold has a generally conical cross-sectional shape. The micro concave portion may have a stepped side surface. It is preferable that the two-dimensional size (opening diameter: D _p ) of the micro concave portion is 10 nm or more and less than 500 nm, and the depth (D _depth ) is about 10 nm or more and less than 1000 nm (1 μm). Moreover, it is preferable that the bottom part of a micro recessed part is sharp (the bottom is a point). Furthermore, it is preferable that the micro concave portions are closely packed, and assuming that the shape of the micro concave portions when viewed from the normal direction of the porous alumina layer is a circle, the adjacent circles overlap each other and the adjacent micro portions are adjacent to each other. It is preferable that a flange is formed between the concave portions. When the substantially conical micro concave portions are adjacent so as to form a collar portion, the two-dimensional size D _p of the micro concave portions is assumed to be equal to the average inter-adjacent distance D _int . Therefore, the moth-eye type porous alumina layer for producing the antireflection film has a dense micro-concave portion with D _p = D _int of 10 nm or more and less than 500 nm and D _depth of 10 nm or more and less than 1000 nm (1 μm). It is preferable to have a regularly arranged structure. Since the shape of the opening of the microscopic recess is not circular strictly, D _p is preferably determined from the SEM image of the surface. The thickness t _p of the porous alumina layer is about 1 μm or less.

  Such a porous alumina layer is formed by alternately repeating anodic oxidation and etching. Specifically, the step of forming a porous alumina layer having a plurality of micro-recesses by anodizing the surface of the aluminum base material, and then bringing the porous alumina layer into contact with the etching solution to form a porous layer. A step of enlarging the plurality of micro-recesses of the alumina layer, and a step of further growing the plurality of micro-recesses by further anodizing. The electrolytic solution used for anodization is, for example, an aqueous solution containing an acid selected from the group consisting of oxalic acid, tartaric acid, phosphoric acid, sulfuric acid, chromic acid, citric acid, and malic acid. As the etching solution, for example, an aqueous solution of organic acid such as phosphoric acid, formic acid, sulfuric acid, acetic acid, citric acid, a mixed aqueous solution of chromic phosphoric acid, or an aqueous solution of alkali such as sodium hydroxide or potassium hydroxide can be used.

  It is preferable that the series of steps of repeating anodization and etching end with the anodization step. By ending with the anodizing step (without performing the subsequent etching step), the bottom of the micro concave portion can be reduced. A method of forming such an inverted moth-eye structure is disclosed in, for example, Patent Document 1 by the present applicant. For reference, the entire disclosure of Patent Document 1 is incorporated herein.

  It is preferable to use a cylindrical (or roll-shaped) mold as the moth-eye mold. When a cylindrical moth-eye mold is used, an antireflection film can be efficiently produced by a roll-to-roll method, as disclosed in Patent Document 2 by the present applicant. For reference, the entire disclosure of Patent Document 2 is incorporated herein.

  One of the advantages of a moth-eye mold utilizing a porous alumina layer is that the moth-eye mold can be manufactured at low cost. However, since the porous alumina layer has a relatively short life, a new moth-eye mold is frequently required. In the cylindrical moth-eye mold, the cylindrical mold substrate has the highest cost. Here, the mold base means an object to be anodized and etched in the mold manufacturing process. The aluminum base material refers to bulk aluminum that can be self-supported in the form of a plate, cylinder, or column.

  Patent Document 3 by the present applicant describes a method for manufacturing a moth-eye mold by forming an inorganic material layer on the surface of an aluminum base material, and anodizing and etching the aluminum film formed on the inorganic material layer. Is disclosed. In this moth-eye mold, an aluminum film portion (referred to as “aluminum remaining layer”) that remains without being anodized under the porous alumina layer is removed by etching, and an aluminum film is formed on the inorganic material layer. Can be recycled. Since the inorganic material layer functions as an etch stop layer when the remaining aluminum layer is etched, it can be recycled relatively easily. For reference, the entire disclosure of Patent Document 3 is incorporated herein.

International Publication No. 2006/059686 International Publication No. 2011/105206 International Publication No. 2011/125486

  However, according to the study by the present inventor, as shown in an experimental example later, in the method described in Patent Document 3, when etching is performed until the remaining aluminum layer is completely removed, unevenness is formed on the surface of the aluminum substrate. There was something to be done. It has been found that this unevenness is due to the etching of the surface of the aluminum base material along the cutting traces formed by cutting the surface of the aluminum base material to make a mirror surface.

  The surface of an aluminum base material that has been mechanically mirror-finished and is preferably used as a metal substrate for a moth-eye mold is formed with a work-affected layer. It is thought that was formed. Therefore, the problem that the above-mentioned unevenness occurs is not limited to cutting with a bite, but is a common problem when using an aluminum base material that has been subjected to mirror finishing accompanied by formation of a work-affected layer. Of mirror processing (polishing technology), mechanical polishing (MP), such as cutting and grinding, and chemical mechanical polishing (CMP), which uses both chemical polishing and mechanical polishing, are processed deterioration layers. With the formation of. In this specification, “mechanical mirror finishing” includes MP and CMP.

  An object of the present invention is to provide a method for recycling a mold having a porous alumina layer manufactured using an aluminum base material that has been subjected to mechanical mirror finishing, such as the above-described mold for moth-eye. .

  A mold recycling method according to an embodiment of the present invention includes an aluminum base material that has been subjected to mechanical mirror finishing, an inorganic material layer formed on a surface of the aluminum base material, and an inorganic material layer formed on the inorganic material layer. An aluminum residual layer and a porous alumina layer formed on the aluminum residual layer, the porous alumina layer formed by anodizing the surface of the aluminum film and the aluminum film remaining without being anodized Preparing a mold having a remaining aluminum layer (a), forming a anodic alumina layer by substantially completely anodizing the aluminum remaining layer of the mold (b), and the process (B) is followed by a step (c) of etching the anodized alumina layer. Here, substantially completely anodizing means, for example, that the area of the aluminum remaining layer is about 10% or less of the total area of the inorganic material layer when viewed from the normal direction of the inorganic material layer. It means to anodize until.

  In one embodiment, the recycling method includes a step (sa1) of etching at least a part of the porous alumina layer before the step (b).

  In one embodiment, the anodic oxidation in the step (b) is performed at a voltage of 35V to 60V.

  In one embodiment, the step (c) is performed using an aqueous phosphoric acid solution.

  In one embodiment, the step (b) is performed using an aqueous oxalic acid solution.

  In one embodiment, the surface of the aluminum base material is cut by cutting.

  In one embodiment, the aluminum substrate is a cylindrical aluminum tube.

  In a certain embodiment, the said process (b) is performed by supplying an electric current from the said aluminum base material side.

  In one embodiment, the inorganic material layer has a thickness of less than 500 nm.

  According to an embodiment of the present invention, there is provided a method for recycling a mold having a porous alumina layer manufactured using an aluminum substrate that has been subjected to mechanical mirror finishing.

(A)-(c) is typical sectional drawing for demonstrating the recycling method of the type | mold by embodiment of this invention. (A)-(c) is a figure for demonstrating the process of removing the aluminum residual layer 18r in the recycling method of the type | mold by embodiment of this invention, (a) is substantially the aluminum residual layer 18r. It is typical sectional drawing which shows the state fully anodized, (b) is the inorganic material layer 16 exposed after removing the anodized alumina layer 18a, and the aluminum residual layer 18r which remained without being anodized. (C) is a SEM image of the sample after removing the anodized alumina layer 18a (full scale 500 nm in the SEM image). (A) is a figure of the image which shows the external appearance of the moth-eye type | mold which removed the aluminum residual layer by the method of patent document 3, (b) is the schematic diagram which expanded the surface of (a). (A) And (b) is the figure of the image of the cross section which observed the surface vicinity of the type | mold shown in Fig.3 (a) with the transmission electron microscope (STEM), (a) is STEM observed at low magnification (B) is an STEM image (full scale 500 nm in the STEM image) observed at a high magnification. (A)-(e) is a figure for demonstrating the manufacturing method of the moth-eye type | mold 100 described in patent document 3, and the structure of the moth-eye type | mold 100. FIG. It is a figure for demonstrating the manufacturing method of the anti-reflective film using the type | mold 100 for moth eyes.

  Hereinafter, a mold recycling method according to an embodiment of the present invention will be described with reference to the drawings.

  The mold recycled by the mold recycling method according to the embodiment of the present invention is, for example, the moth-eye mold described in Patent Document 3. With reference to FIG. 5, the manufacturing method and structure of the moth-eye mold 100 described in Patent Document 3 will be described.

  FIGS. 5A to 5E are schematic cross-sectional views for explaining a method for manufacturing the moth-eye mold 100 that is recycled by the mold recycling method according to the embodiment of the present invention.

  First, as shown in FIG. 5A, as a mold base, an aluminum base 12, an inorganic material layer 16 formed on the surface of the aluminum base 12, and aluminum deposited on the inorganic material layer 16. A mold substrate 10 having a film 18 is prepared.

  As the aluminum substrate 12, a relatively rigid aluminum substrate having an aluminum purity of 99.50 mass% or more and less than 99.99 mass% is used. As impurities contained in the aluminum substrate 12, iron (Fe), silicon (Si), copper (Cu), manganese (Mn), zinc (Zn), nickel (Ni), titanium (Ti), lead (Pb) It is preferable that at least one element selected from the group consisting of tin (Sn) and magnesium (Mg) is included, and Mg is particularly preferable. The mechanism by which pits (dents) are formed in the etching process is a local cell reaction, and therefore ideally contains no element nobler than aluminum and is a base metal, Mg (standard electrode potential is − It is preferable to use an aluminum substrate 12 containing 2.36V) as an impurity element. If the content of an element nobler than aluminum is 10 ppm or less, it can be said that the said element is not included substantially from an electrochemical viewpoint. The Mg content is preferably 0.1% by mass or more, and more preferably in the range of about 3.0% by mass or less. If the Mg content is less than 0.1 mass%, sufficient rigidity cannot be obtained. On the other hand, when the content rate increases, Mg segregation easily occurs. Even if segregation occurs in the vicinity of the surface forming the moth-eye mold, there is no electrochemical problem. However, Mg forms an anodic oxide film having a form different from that of aluminum, which causes defects. What is necessary is just to set suitably the content rate of an impurity element according to the rigidity required according to the shape of the aluminum base material 12, thickness, and a magnitude | size. For example, when the plate-shaped aluminum substrate 12 is produced by rolling, an appropriate Mg content is about 3.0 mass%, and the aluminum substrate 12 having a three-dimensional structure such as a cylinder is produced by extrusion. When it does, it is preferable that the content rate of Mg is 2.0 mass% or less. If the Mg content exceeds 2.0 mass%, extrusion processability generally decreases.

  As the aluminum substrate 12, for example, a cylindrical aluminum tube formed of JIS A1050, Al—Mg alloy (for example, JIS A5052), or Al—Mg—Si alloy (for example, JIS A6063) is used.

  The surface of the aluminum base 12 is preferably subjected to bite cutting. If, for example, abrasive grains remain on the surface of the aluminum base 12, electrical conduction between the aluminum film 18 and the aluminum base 12 is facilitated in a portion where the abrasive grains exist. In addition to the abrasive grains, where there are irregularities, local conduction between the aluminum film 18 and the aluminum substrate 12 is likely to occur. When local conduction is made between the aluminum film 18 and the aluminum base 12, there is a possibility that a battery reaction occurs locally between the impurities in the aluminum base 12 and the aluminum film 18.

As a material of the inorganic material layer 16, for example, tantalum oxide (Ta ₂ O ₅ ) or silicon dioxide (SiO ₂ ) can be used. The inorganic material layer 16 can be formed by sputtering, for example. When a tantalum oxide layer is used as the inorganic material layer 16, the thickness of the tantalum oxide layer is, for example, 200 nm.

  The thickness of the inorganic material layer 16 is preferably 100 nm or more and less than 500 nm. If the thickness of the inorganic material layer 16 is less than 100 nm, defects (mainly voids, that is, gaps between crystal grains) may occur in the aluminum film 18 in some cases. Further, when the thickness of the inorganic material layer 16 is 500 nm or more, the aluminum base 12 and the aluminum film 18 are easily insulated from each other depending on the surface state of the aluminum base 12. In order to anodize the aluminum film 18 by supplying current to the aluminum film 18 from the aluminum substrate 12 side, it is necessary that a current flow between the aluminum substrate 12 and the aluminum film 18. If a configuration is adopted in which current is supplied from the inner surface of the cylindrical aluminum substrate 12, it is not necessary to provide an electrode on the aluminum film 18, so that the aluminum film 18 can be anodized over the entire surface, and the current is increased as the anodization proceeds. Therefore, the aluminum film 18 can be uniformly anodized over the entire surface without causing a problem that it is difficult to be supplied.

  In order to form the thick inorganic material layer 16, it is generally necessary to lengthen the film formation time. When the film formation time is lengthened, the surface temperature of the aluminum base 12 is unnecessarily increased. As a result, the film quality of the aluminum film 18 is deteriorated, and defects (mainly voids) may occur. If the thickness of the inorganic material layer 16 is less than 500 nm, the occurrence of such a problem can be suppressed.

  The aluminum film 18 is, for example, a film formed of aluminum having a purity of 99.99 mass% or more (hereinafter, also referred to as “high-purity aluminum film”) as described in Patent Document 3. The aluminum film 18 is formed using, for example, a vacuum deposition method or a sputtering method. The thickness of the aluminum film 18 is preferably in the range of about 500 nm or more and about 1500 nm or less, for example, about 1 μm.

  As the aluminum film 18, an aluminum alloy layer described in International Publication No. 2013/0183576 may be used instead of the high-purity aluminum film. The aluminum alloy layer described in International Publication No. 2013/0183576 contains aluminum, a metal element other than aluminum, and nitrogen. In this specification, the “aluminum film” includes not only a high-purity aluminum film but also an aluminum alloy layer described in International Publication No. 2013/0183576. For reference purposes, the entire disclosure of WO2013 / 0183576 is incorporated herein by reference.

  When the aluminum alloy layer is used, a mirror surface having a reflectance of 80% or more can be obtained. The average grain size of the crystal grains constituting the aluminum alloy layer when viewed from the normal direction of the aluminum alloy layer is, for example, 100 nm or less, and the maximum surface roughness Rmax of the aluminum alloy layer is 60 nm or less. The content rate of nitrogen contained in the aluminum alloy layer is, for example, not less than 0.5 mass% and not more than 5.7 mass%. The absolute value of the difference between the standard electrode potential of a metal element other than aluminum contained in the aluminum alloy layer and the standard electrode potential of aluminum is 0.64 V or less, and the content of the metal element in the aluminum alloy layer is 1.0 mass. % Or more and 1.9 mass% or less is preferable. The metal element is, for example, Ti or Nd. However, the metal element is not limited to this, and other metal elements whose absolute value of the difference between the standard electrode potential of the metal element and the standard electrode potential of aluminum is 0.64 V or less (for example, Mn, Mg, Zr, V, and Pb). Furthermore, the metal element may be Mo, Nb, or Hf. The aluminum alloy layer may contain two or more of these metal elements. The aluminum alloy layer is formed by, for example, a DC magnetron sputtering method. The thickness of the aluminum alloy layer is also preferably in the range of about 500 nm to about 1500 nm, for example, about 1 μm.

  Next, as shown in FIG. 5B, the porous alumina layer 14 having a plurality of micro-recesses (pores) 14p is formed by anodizing the surface 18s of the aluminum film 18. The porous alumina layer 14 includes a porous layer having a micro concave portion 14p and a barrier layer (the bottom of the concave portion (pore) 14p). It is known that the interval between the adjacent micro concave portions 14p (center-to-center distance) corresponds to approximately twice the thickness of the barrier layer and is approximately proportional to the voltage during anodization. The porous alumina layer 14 is formed, for example, by anodizing the surface 18s in an acidic electrolytic solution. The electrolytic solution used in the step of forming the porous alumina layer 14 is an aqueous solution containing an acid selected from the group consisting of oxalic acid, tartaric acid, phosphoric acid, sulfuric acid, chromic acid, citric acid, and malic acid, for example. For example, the porous alumina layer 14 is formed by anodizing the surface 18 s of the aluminum film 18 using an oxalic acid aqueous solution (concentration 0.3 mass%, liquid temperature 10 ° C.) at an applied voltage of 80 V for 55 seconds.

  Next, as shown in FIG. 5 (c), the porous alumina layer 14 is brought into contact with an alumina etchant and etched by a predetermined amount to enlarge the opening of the micro concave portion 14p. By adjusting the type / concentration of the etchant and the etching time, the etching amount (that is, the size and depth of the micro-recess 14p) can be controlled. As an etchant, for example, 10 mass% phosphoric acid, an organic acid such as formic acid, acetic acid, or citric acid, an aqueous solution of sulfuric acid, or a mixed aqueous solution of chromic phosphoric acid can be used. For example, etching is performed for 20 minutes using a phosphoric acid aqueous solution (10 mass%, 30 ° C.).

  Next, as shown in FIG. 5 (d), the aluminum film 18 is partially anodized again to grow the micro-concave portions 14p in the depth direction and to thicken the porous alumina layer 14. Here, the growth of the micro concave portion 14p starts from the bottom of the already formed micro concave portion 14p, and therefore the side surface of the micro concave portion 14p is stepped.

  Thereafter, if necessary, the porous alumina layer 14 is further etched by bringing it into contact with an alumina etchant to further expand the hole diameter of the micro concave portion 14p. As the etchant, it is preferable to use the above-described etchant, and in practice, the same etch bath may be used.

  In this way, by repeating the above-described anodizing step and etching step a plurality of times alternately (for example, 5 times: anodizing 5 times and etching 4 times), as shown in FIG. The moth-eye mold 100 having the porous alumina layer 14 having a shape is obtained. Under the porous alumina layer 14, an aluminum remaining layer 18r that has not been anodized in the aluminum film 18 is present.

  Next, with reference to FIG. 6, a method for manufacturing an antireflection film using the moth-eye mold 100 will be described. FIG. 6 is a schematic cross-sectional view for explaining a method for producing an antireflection film by a roll-to-roll method.

  First, a cylindrical moth-eye mold 100 is prepared. The cylindrical moth-eye mold 100 is manufactured, for example, by the manufacturing method described with reference to FIG.

  As shown in FIG. 6, ultraviolet light (UV) is applied to the ultraviolet curable resin 32 ′ by irradiating the ultraviolet curable resin 32 ′ with the workpiece 42 with the ultraviolet curable resin 32 ′ pressed against the moth-eye mold 100. The cured resin 32 ′ is cured. As the ultraviolet curable resin 32 ′, for example, an acrylic resin can be used. The workpiece 42 is, for example, a TAC (triacetyl cellulose) film. The workpiece 42 is unwound from an unillustrated unwinding roller, and thereafter, an ultraviolet curable resin 32 ′ is applied to the surface by, for example, a slit coater. The workpiece 42 is supported by support rollers 46 and 48 as shown in FIG. The support rollers 46 and 48 have a rotation mechanism and convey the workpiece 42. The cylindrical moth-eye mold 100 is rotated in a direction indicated by an arrow in FIG. 6 at a rotation speed corresponding to the conveyance speed of the workpiece 42.

  Thereafter, by separating the moth-eye mold 100 from the workpiece 42, a cured product layer 32 to which the uneven structure (inverted moth-eye structure) of the moth-eye mold 100 is transferred is formed on the surface of the workpiece 42. . The workpiece 42 having the cured product layer 32 formed on the surface is wound up by a winding roller (not shown).

  While the antireflection film is manufactured, the porous alumina layer 14 of the moth-eye mold 100 is worn and / or damaged, and the quality of the antireflection film is deteriorated. A new moth-eye mold is produced by recycling a moth-eye mold that is no longer able to produce an antireflection film of a desired quality.

  Here, the result of examining the recycling method described in Patent Document 3 (hereinafter referred to as “reference experiment example”) will be described.

(Reference experiment example)
According to the recycling method described in Patent Document 3, the aluminum remaining layer 18r remaining without being anodized under the porous alumina layer 14 is removed by etching, and a new aluminum film 18 is formed on the inorganic material layer 16. Thus, a new mold base 10 is obtained.

  With reference to FIG. 6, the moth-eye mold 100 manufactured according to the method exemplified in the description with reference to FIG. 5 (anodic oxidation: oxalic acid aqueous solution (concentration: 0.3 mass%), etching: 10 mass% phosphoric acid aqueous solution) was used. The moth-eye mold 100u after the antireflection film was produced according to the method was used as a sample for recycling.

The aluminum substrate 12 of the moth-eye mold 100u is made of an aluminum tube (diameter) of an Al—Mg—Si alloy (JIS A6063, Si: 0.4%, Mg: 0.5%) whose surface is cut by cutting. : About 200 mm, length: 1000 mm, thickness: about 10 mm), the thickness of the inorganic material layer (here, tantalum oxide (Ta ₂ O ₅ ) layer) 16 is about 200 nm, and the thickness of the porous alumina layer 14 The thickness of the aluminum residual layer 18r was about 350 nm.

As an etchant for removing the remaining aluminum layer 18r, an aqueous phosphoric acid solution was used among various aqueous solutions used for general aluminum etching. As the phosphoric acid aqueous solution, 36 mass% and 85 mass% phosphoric acid aqueous solutions were used, the liquid temperature (etching temperature) was set to 22 ° C. or 30 ° C., and etching was performed under the following conditions.
Condition 1: phosphoric acid 36 mass%, 22 ° C., etching time (5 minutes, 15 minutes, 60 minutes, 120 minutes, 600 minutes)
Condition 2: phosphoric acid 36 mass%, 30 ° C., etching time (5 minutes, 15 minutes, 60 minutes, 120 minutes, 180 minutes, 300 minutes)
Condition 3: phosphoric acid 85 mass%, 22 ° C., etching time (10 minutes, 30 minutes, 60 minutes, 120 minutes)

  About the sample of 600 minutes on condition 1, 180 minutes and 300 minutes on condition 2, and 120 minutes on condition 3, the aluminum residual layer 18r was removed substantially completely and the tantalum oxide layer 16 was exposed. When the tantalum oxide layer (having a thickness of about 200 nm) 16 was exposed, a light blue interference color was observed. Therefore, a simple determination as to whether or not the remaining aluminum layer 18r on the tantalum oxide layer 16 was substantially completely removed was made visually.

  An image showing the appearance of these samples is shown in FIG. 3 (a), and a schematic diagram enlarging the surface of FIG. 3 (a) is shown in FIG. 3 (b). The white trace in FIG. 3A is a linear trace parallel to the circumferential direction of the cylindrical mold, as schematically shown in FIG. This linear trace is considered to be formed along the cutting trace by the cutting process for mirroring the surface of the aluminum base 12.

  FIG. 4 shows an image observed by a transmission electron microscope (STEM) after cutting a sample in a direction perpendicular to the linear marks in FIG. As is clear from FIG. 4, a gap (a portion observed in white) is formed between the aluminum base 12 and the tantalum oxide layer 16. This void is formed as a result of the etching solution (phosphoric acid aqueous solution) for removing the aluminum residual layer 18r entering between the aluminum base 12 and the tantalum oxide layer 16 and corroding the surface of the aluminum base 12. It is thought. That is, in the tantalum oxide layer 16 having a thickness of about 200 nm, it is considered that defects that allow the etching solution to pass through are distributed along the cutting marks on the surface of the aluminum base 12. In addition, this defect serves as a current path when anodizing the remaining aluminum layer 18r in a recycling method according to an embodiment of the present invention described later.

  As described above, when the aluminum substrate 12 subjected to mechanical mirror finishing is used and the inorganic material layer 16 is thin (for example, less than 500 nm), the aluminum remaining layer described in Patent Document 3 is used. When the method of removing 18r by etching is adopted, there arises a problem that a portion of the surface of the aluminum base 12 corresponding to a mark by mechanical mirror finishing (a portion where a work-affected layer is formed) is corroded. Found that there is a case.

  When an experiment similar to that described above was performed using an aqueous phosphorous acetate solution and an aqueous sodium hydroxide solution as an aluminum etching solution, the surface of the aluminum base 12 was used in the same manner as when using an aqueous phosphoric acid solution as the etching solution. However, there was a problem that the portion corresponding to the trace by mechanical mirror finishing was corroded.

  In order to solve the above problem, the mold recycling method according to the embodiment of the present invention includes a step of forming the anodized alumina layer 18a by substantially completely anodizing the aluminum residual layer 18r, and thereafter Etching the anodized alumina layer 18a. That is, in the recycling method of Patent Document 3, aluminum is etched, whereas in the recycling method according to the embodiment of the present invention, the anodized alumina layer 18a formed by anodizing the aluminum residual layer 18r is etched. The etching solution for the anodized alumina layer 18a does not etch aluminum or the etching rate is slow, so that the surface of the aluminum base 12 is not etched.

  A mold recycling method according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. 1A to 1C are schematic sectional views for explaining a mold recycling method according to an embodiment of the present invention, and FIGS. 2A to 2C are embodiments of the present invention. It is a figure for demonstrating the process of removing the aluminum residual layer 18r in the recycling method of the type | mold by.

  As shown in FIG. 1A, an aluminum base material 12 that has been subjected to mechanical mirror finishing, an inorganic material layer 16 formed on the surface of the aluminum base material 12, and an inorganic material layer 16 are formed. The remaining aluminum layer 18r and the porous alumina layer 14 formed on the remaining aluminum layer 18r, anodized within the porous alumina layer 14 and the aluminum film 18 formed by anodizing the surface of the aluminum film 18. A mold 100u having a remaining aluminum remaining layer 18r is prepared. This mold is, for example, after using the moth-eye mold 100 described above, and as a result of the use, the porous alumina layer 14 is worn and / or damaged.

  Next, as shown in FIG. 1B, the remaining aluminum layer 18r is completely anodized to form an anodized alumina layer 18a. On the inorganic material layer 16 of the anodic oxidation type 110 thus obtained, only the porous alumina layer 14 and the anodic oxidation alumina layer 18a exist. That is, only anodized alumina is present on the inorganic material layer 16. As will be described later with reference to FIGS. 2A to 2C, it is not always necessary to completely anodize the remaining aluminum layer 18r, as long as it does not adversely affect the reproduction of the mold base 10. For example, a part of the aluminum remaining layer 18r may remain without being anodized.

  Next, as shown in FIG. 1C, the anodized alumina layer 18a is etched. At this time, the porous alumina layer 14 is also etched. The porous alumina layer 14 does not need to be completely etched as long as the surface of the inorganic material layer 16 can be exposed. If the anodized alumina layer 18a is removed by etching, it is formed on the anodized alumina layer 18a. The porous alumina layer 14 is inevitably removed. As an etching solution for anodized alumina, for example, 10 mass% phosphoric acid, an organic acid aqueous solution such as formic acid, acetic acid, citric acid, or a chromic phosphoric acid mixed aqueous solution can be used. At this time, when a tantalum oxide layer or a silicon dioxide layer is used as the inorganic material layer 16, these inorganic materials are not etched by the etching solution for anodized alumina, so that the inorganic material layer 16 functions as an etch stop layer. . In addition, since the aluminum base 12 is not substantially etched with the anodized alumina etching solution, the surface of the aluminum base 12 is maintained in a mirror-finished state.

  In this way, the base 120 of the mold base for recycling is obtained in which the surface of the inorganic material layer 16 formed on the aluminum base 12 is exposed.

  By forming the aluminum film 18 on the inorganic material layer 16 of the obtained base 120, the mold base 10 shown in FIG. 5A is obtained. If necessary, an inorganic material may be deposited on the inorganic material layer 16.

  In FIG. 1B, the remaining aluminum layer 18r is completely anodized to form an anodized alumina layer 18a. In FIG. 1C, the anodized alumina layer 18a (and the porous alumina layer 14) are completely removed. Although the example to do was shown, it is not restricted to this. Of course, in order to completely remove the remaining aluminum layer 18r, it is preferable to completely anodize the remaining aluminum layer 18r, but it is not always necessary to completely anodize the remaining aluminum layer 18r. What is necessary is just to anodize substantially completely to such an extent that it does not have a bad influence on reproduction.

  As schematically shown in FIG. 2A, in the anodized alumina layer 18a formed by anodizing the aluminum residual layer 18r, the bottom (barrier layer) of the recess (pore) 14p grows downward. Formed as follows. Since the bottom surface of the bottom of the micro concave portion 14p is substantially hemispherical, an aluminum remaining layer 18r that is not anodized easily remains between the adjacent micro concave portions 14p.

  When the anodized alumina layer 18a is removed by etching with a part of the remaining aluminum layer 18r remaining, the inorganic exposed after removing the anodized alumina layer 18a as schematically shown in FIG. Between the material layers 16, there is an aluminum remaining layer 18r that remains without being anodized. When the area of the remaining portion of the aluminum remaining layer 18r that is not anodized exceeds about 10% of the total area of the inorganic material layer 16 when viewed from the normal direction of the inorganic material layer 16, it When the moth-eye mold 100 is reproduced using the mold base 10 that is reproduced by depositing the aluminum film 18, the aluminum film 18 may be corroded. Therefore, when viewed from the normal direction of the inorganic material layer 16, the area of the remaining portion of the aluminum remaining layer 18 r that is not anodized is about 10% or less of the total area of the inorganic material layer 16. The aluminum remaining layer 18r may be anodized.

  FIG. 2C is an SEM image (full scale 500 nm in the SEM image) of the sample after removing the anodized alumina layer 18a without completely anodizing the remaining aluminum layer 18r. Ring-shaped dotted white portions are the remaining aluminum layer 18r remaining without being anodized. Thus, if the area of the remaining portion of the remaining aluminum layer 18r that has not been anodized is about 10% or less of the total area of the inorganic material layer 16, the aluminum film 18 of the regenerated moth-eye mold 100 is used. There is no corrosion.

  In addition, the step of etching the anodized alumina layer 18a formed by anodizing the aluminum remaining layer 18r substantially completely removes the anodized alumina layer 18a and exposes the surface of the inorganic material layer 16. It is this process. “Substantially completely remove” includes “completely remove” and “completely remove” to the extent that there is no significant difference in the final result. The anodized alumina layer 18a formed by anodizing the aluminum residual layer 18r is typically completely removed, but this is not always necessary, and a part of the anodized alumina layer 18a is substantially formed. It may remain. Even if a part of the anodized alumina layer is present on the inorganic material layer 16, it can be used as a mold substrate. Furthermore, what deposited the inorganic material on a part of anodic oxidation alumina layer which remained on the inorganic material layer can also be used as a mold base.

  Of course, the remaining aluminum layer 18r can be completely anodized by increasing the anodizing time. Further, by using an electrolyte of a different type from the electrolyte in the anodizing step for producing the moth-eye mold (for example, an electrolyte close to neutrality), the remaining aluminum layer 18r can be more completely anodized more reliably. However, since it may be accompanied by an increase in cost and a decrease in productivity, it is preferable to use the same electrolytic solution as that used for anodization for producing a moth-eye mold.

  Note that the step of anodizing the aluminum residual layer 18r described with reference to FIG. 1B is realized by passing a current from the aluminum base 12 to the aluminum residual layer 18r through the inorganic material layer 16. Because. As described above, it is considered that a defect is generated in a portion of the inorganic material layer 16 corresponding to a mark by mechanical mirror processing of the aluminum substrate 12, and this defect is a current path. It is done. Therefore, the inorganic material layer 16 preferably has appropriate conductivity in the thickness direction. For this purpose, for example, when the tantalum oxide layer 16 is used as the inorganic material layer 16, the thickness of the tantalum oxide layer 16 is, for example, not less than 100 nm and less than 500 nm.

  The voltage for anodizing the aluminum residual layer 18r depends on the thickness of the barrier layer that the porous alumina layer 14 has. In order to anodize the remaining aluminum layer 18r using the same electrolytic solution as the anodizing step for forming the porous alumina layer 14, a voltage higher than the voltage in the anodizing step for forming the porous alumina layer 14 is used. Need to be applied. Therefore, in order to make the voltage for anodizing the aluminum residual layer 18r relatively low, the thickness of the barrier layer is reduced by etching a part of the porous alumina layer 14 prior to the anodization. It is preferable. Further, as will be described later with reference to experimental examples, for example, when anodic oxidation for forming the moth-eye mold 100 is performed at 80V, a part of the porous alumina layer 14 is etched, and the aluminum remaining layer 18r is reduced to 35V. When the anodic oxidation is performed at a voltage of 60 V or less, the aluminum remaining layer 18r can be anodized substantially efficiently, that is, in a short time.

  In addition, by etching at least a part of the porous alumina layer 14 prior to the anodic oxidation of the remaining aluminum layer 18r, it is possible to stably perform the etching without being affected by the residue of the resin adhering to the surface of the porous alumina layer 14. There is also an advantage that the subsequent steps can be performed.

  Anodization is performed using, for example, an oxalic acid aqueous solution as the electrolytic solution. Depending on the application of the mold, the size and depth of the opening of the micro concave portion 14p of the porous alumina layer 14, the distance between adjacent micro concave portions 14p, and the arrangement of the micro concave portions 14p are different. The applied voltage can be changed as appropriate. Etching of the anodized alumina layer 18a is performed using, for example, a phosphoric acid aqueous solution. The electrolytic solution used for anodization is, for example, an aqueous solution containing an acid selected from the group consisting of oxalic acid, tartaric acid, phosphoric acid, sulfuric acid, chromic acid, citric acid, and malic acid. As an etching solution, an aqueous solution of an organic acid such as formic acid, acetic acid, or citric acid or an aqueous solution of sulfuric acid, a mixed aqueous solution of chromic phosphoric acid, or an aqueous solution of an alkali such as sodium hydroxide or potassium hydroxide can be used.

  The mold recycling method according to the embodiment of the present invention will be described in detail below by showing experimental examples. Also in the following experimental examples, the moth-eye mold 100u prepared in the same manner as the above-described reference experimental example was used as a mold sample.

(Experimental example 1)
A small piece was cut out from the moth-eye mold 100u described above, and it was studied to anodize the aluminum residual layer 18r of the moth-eye mold 100u under the same conditions as those in the anodic oxidation process for producing the moth-eye mold 100. That is, the aluminum residual layer 18r of the moth-eye mold 100u was anodized at an applied voltage of 80 V using an aqueous oxalic acid solution (concentration: 0.3 mass%, liquid temperature: 10 ° C.) as an electrolytic solution. Moreover, phosphoric acid aqueous solution (10 mass%, 30 degreeC) was used for the etching of the anodized alumina layer 18a. According to the experiments by the present inventors, the etching rate of the aqueous phosphoric acid solution (10 mass%, 30 ° C.) with respect to aluminum was not more than 1/7 of the etching rate with respect to the anodized alumina.

  The anodizing time was changed to 300 seconds, 800 seconds, 1200 seconds, 1600 seconds, 2400 seconds, 60 minutes and 90 minutes, and the etching time was changed to 30 minutes, 60 minutes, 90 minutes, 120 minutes, 150 minutes, 300 minutes. Changed with minutes. When the anodizing time was 800 seconds or longer and the etching time was 90 minutes or longer, the anodized alumina layer 18a could be removed substantially completely. When the anodized alumina layer 18a was substantially completely removed and the tantalum oxide layer (thickness approximately 200 nm) 16 was exposed, a light blue interference color was observed. Therefore, as in the reference experimental example, a simple determination was made visually as to whether or not the anodized alumina layer 18a on the tantalum oxide layer 16 was substantially completely removed. When the remaining aluminum layer 18r was anodized, a green interference color was observed.

  When the anodizing time was 800 seconds or longer and the etching time was 90 minutes or longer, the anodized alumina layer 18a could be substantially completely removed. However, cutting traces could be visually observed. . This cut mark is due to the formation of a gap between the aluminum base 12 and the tantalum oxide layer 16. The only traces that were not observed were samples with an anodization time of 90 minutes and an etching time of 90 minutes. From this, in order to anodize the aluminum residual layer 18r substantially completely at the same voltage (80V) as the voltage of the anodizing step for forming the porous alumina layer 14, a long time of 90 minutes or more is required. I found that it was necessary.

(Experimental example 2)
By reducing the thickness of the barrier layer of the porous alumina layer 14, an attempt was made to lower the voltage required when anodizing the remaining aluminum layer 18r. In the same manner as in Reference Experiment Example and Experiment Example 1, a small piece was cut out from the above moth-eye mold 100u to obtain a mold sample.

  The porous alumina layer 14 was etched before the remaining aluminum layer 18r of the mold sample was anodized. Etching before anodization may be referred to as “pre-etching”. As the pre-etching etchant, the same phosphoric acid aqueous solution (10 mass%, 30 ° C.) as the etching solution of Experimental Example 1 was used. The pre-etching time was 5 minutes, 15 minutes, 30 minutes, 45 minutes, 60 minutes, 90 minutes, 120 minutes and 180 minutes. About each type | mold sample which performed the pre-etching, the aluminum residual layer 18r was anodized for 60 minutes with the applied voltage of 45V using the oxalic-acid aqueous solution (concentration 0.3mass%, liquid temperature 10 degreeC). Thereafter, the anodized alumina layer 18a was etched for 90 minutes using an aqueous phosphoric acid solution (10 mass%, 30 ° C.).

  For the mold samples with pre-etching times of 5 minutes, 15 minutes, and 30 minutes, the tantalum oxide layer 16 could not be substantially completely exposed even when anodic oxidation and etching were performed under the above conditions. For the mold sample having a pre-etching time of 45 minutes or longer, the tantalum oxide layer 16 could be substantially completely exposed by anodizing and etching under the above conditions. However, cutting traces were observed on the surface of the mold sample with a pre-etching time of 180 minutes. In the mold sample with a pre-etching time of 180 minutes, a light blue interference color was observed at the stage when the pre-etching was completed. At this time, the porous alumina layer 14 and the aluminum remaining layer 18r were substantially completely formed. It can be seen that it has been removed. Therefore, in the mold sample having a pre-etching time of 180 minutes, the etching solution penetrates between the aluminum base 12 and the tantalum oxide layer 16 in the pre-etching stage, as described in the reference experimental example. It is considered that the surface of the aluminum substrate 12 was corroded and voids were formed.

  From the above, it was confirmed that the anodic oxidation voltage can be reduced by performing pre-etching. Further, in order to anodize the aluminum residual layer 18r at 45V, the pre-etching time is preferably 45 minutes or more, and in order to prevent the occurrence of cutting marks, it is preferably less than 180 minutes. I understood.

  In addition, although it examined also performing anodizing at 30V, the conditions which can prevent generation | occurrence | production of a cutting trace were not found. Specifically, after the pre-etching is performed for 90 minutes or more and then anodized at 30 V for 60 minutes or more, the remaining aluminum layer 18r can be substantially completely anodized. The remaining aluminum layer 18r could be substantially completely removed by etching for more than a minute, but all showed cutting marks.

  The preferred range of the anodic oxidation voltage and time will be described in detail in Experimental Example 4.

(Experimental example 3)
A preferred range of anodizing time and etching time was studied. Similarly to the reference experimental example and the experimental examples 1 and 2, a small piece was cut out from the above moth-eye mold 100u, and an aqueous phosphoric acid solution (10 mass%, 30 ° C.) was used as the pre-etching etchant as in the experimental example 2. The pre-etching time was 60 minutes. For anodization, an aqueous oxalic acid solution (concentration 0.3 mass%, liquid temperature 10 ° C.) was used, the anodization voltage was 45 V, and the anodization time was 13 minutes 20 seconds, 30 minutes, 60 minutes, 90 minutes, 120 minutes. The etching time was changed to 60 minutes, 90 minutes, and 120 minutes.

  No cutting marks were observed in the sample having an anodizing time of 60 minutes or longer and an etching time of 60 minutes or longer. Of the samples having an anodizing time of 13 minutes 20 seconds and 30 minutes, no cutting marks were observed in the samples having an etching time of 60 minutes, but there were no cutting marks in the samples having an etching time of 90 minutes and 120 minutes. It was seen.

  Further, samples were prepared in which the anodic oxidation time was 60 minutes and the etching time was changed to 30 minutes, 60 minutes, 90 minutes, 120 minutes, 180 minutes, and 300 minutes. The sample having an etching time of 30 minutes was green, and it was found that the anodized alumina layer 18a was not completely removed. All samples with an etching time of 60 minutes or more were light blue, the anodized alumina layer 18a was substantially completely removed, and no cutting traces were observed.

  From the above, considering the process margin and the like, it can be said that the anodic oxidation time is preferably 60 minutes or longer and the etching time is preferably 60 minutes or longer.

(Experimental example 4)
The preferred range of anodizing voltage and time was examined in detail. In the same manner as in Reference Experimental Example and Experimental Examples 1 and 2, a small piece was cut out from the above moth-eye mold 100u to obtain a mold sample. As in Experimental Example 2, a phosphoric acid aqueous solution (10 mass%, 30 ° C.) was used as the etching solution, and the pre-etching time was 60 minutes (however, the pre-etching time of the sample having an anodic oxidation voltage of 30 V was 90 minutes. 2), and the etching time after anodization was 90 minutes. For anodization, an oxalic acid aqueous solution (concentration: 0.3 mass%, liquid temperature: 10 ° C.) was used, and the anodization voltage and time were changed. The obtained results are shown in Table 1 below. Numbers in parentheses indicate non-defective product / number of samples. As in the above-described experimental example, the non-defective product was determined as a non-defective product condition in which the anodized alumina layer 18a was substantially completely removed and no cutting trace was visually observed. In addition, “-” in Table 1 indicates that the operation has not been performed.

  It is first understood from the results in Table 1 that the anodic oxidation voltage needs to be higher than 30V and is preferably 35V or higher. The anodic oxidation voltage needs to be 80 V or less, which is an anodic oxidation voltage for forming the moth-eye type porous alumina layer, and is preferably less than 80 V.

  The anodizing time depends on the anodizing voltage. When the anodizing voltage is 35 V or more and less than 60 V, the anodizing time is preferably 60 minutes or more. When the anodic oxidation voltage is more than 40V and less than 50V, particularly 45V, good results can be obtained with an anodic oxidation time of 45 minutes or more. When the anodization voltage is 60 V or more and 70 V or less, the anodization time is preferably 90 minutes or more. From the results of Experimental Example 3, the upper limit of the anodizing time exceeds at least 300 minutes. Therefore, actually, from the viewpoint of shortening the process time, the anodic oxidation time is set to 90 minutes or less, for example. The experimental results (12) in the shaded area in Table 1 correspond to a preferred embodiment under the conditions exemplified here.

  Resin residues may be present on the surface of the moth-eye mold 100u after the antireflection film is manufactured. It has also been found that the above pre-etching provides the advantage of eliminating the effects of resin residues.

  Here, an example of using a oxalic acid aqueous solution as an electrolytic solution and a phosphoric acid aqueous solution as an etching solution is shown to explain the mold recycling method according to the embodiment of the present invention, but the electrolytic solution and the etching solution are not limited thereto. Absent. As the electrolytic solution, an aqueous solution containing an acid selected from the group consisting of oxalic acid, tartaric acid, phosphoric acid, chromic acid, citric acid and malic acid exemplified above can be used, and as the etching solution, phosphoric acid, An aqueous solution of an organic acid such as formic acid, acetic acid or citric acid, a mixed aqueous solution of chromic phosphoric acid, or an aqueous solution of an alkali such as sodium hydroxide or potassium hydroxide can be used. Although the optimum conditions may vary depending on the type of the electrolytic solution and the etching solution, those skilled in the art can easily obtain the optimum conditions based on the above experimental example.

  Furthermore, although the mold illustrated here is a moth-eye mold, the mold recycling method according to the embodiment of the present invention is not limited to this, and can be widely applied to a mold having a porous alumina layer. For example, it is well known that a mold in which micro concave portions are regularly arranged is formed by adjusting the conditions of anodization when forming a porous alumina layer.

  INDUSTRIAL APPLICABILITY The present invention can be widely used as a recycling method for a mold having a porous alumina layer manufactured using an aluminum base material subjected to mechanical mirror finishing.

10 type base material 12 aluminum base material 14 porous alumina layer 14p micro recessed part (pore)
16 Inorganic material layer 18 Aluminum film 18a Anodized alumina layer (layer obtained by anodizing the remaining aluminum layer)
18r aluminum remaining layer 18s surface of aluminum film 100, 100u moth-eye mold 120 base

Claims (9)

Formed on an aluminum base material subjected to mechanical mirror finishing, an inorganic material layer formed on the surface of the aluminum base material, an aluminum residual layer formed on the inorganic material layer, and the aluminum residual layer Preparing a mold having a porous alumina layer formed by anodizing the surface of an aluminum film and an aluminum remaining layer remaining unanodized in the aluminum film (A) and
Forming an anodized alumina layer by substantially completely anodizing the remaining aluminum layer on the inorganic material layer of the mold; and
(C) after the step (b), exposing the surface of the inorganic material layer by etching the anodized alumina layer ;
A method for recycling a mold substrate , comprising the step (d) of forming an aluminum film on the inorganic material layer after the step (c) . The method for recycling a mold substrate according to claim 1, comprising a step (sa1) of etching at least a part of the porous alumina layer before the step (b). The method for recycling a mold substrate according to claim 1 or 2, wherein the anodic oxidation in the step (b) is performed at a voltage of 35V to 60V. The said process (c) is a recycling method of the mold base material in any one of Claim 1 to 3 performed using phosphoric acid aqueous solution. The said process (b) is the recycling method of the mold base material in any one of Claim 1 to 4 performed using oxalic acid aqueous solution. The mold substrate recycling method according to any one of claims 1 to 5, wherein the surface of the aluminum substrate is cut by cutting. The recycling method for a mold substrate according to any one of claims 1 to 6, wherein the aluminum substrate is a cylindrical aluminum tube. The said process (b) is a recycling method of the mold base material in any one of Claim 1 to 7 performed by supplying an electric current from the said aluminum base material side. The method for recycling a mold substrate according to any one of claims 1 to 8, wherein the inorganic material layer has a thickness of less than 500 nm.

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